Does this mean that Mac users using Safari are safe because the rules were relaxed to allow this?
As several here have already noted, the only requirement is that you click a specially formatted link to visit a specific web page that makes the exploit run. This means that I could make some link like
this and if you clicked on it, it could run some malicous code on your system, possibly opening up your machine. Then mayber I could record your IP address on my page and then hack into your system knowing that you have been exploited. This is all assuming that I knew how to craft the exploit. But none of us do, because it hasn't been disclosed (yet).
All the relaxing of the rules allowed was the simulation of a careless user instead.
Not true. If you go to web pages in Safari, then it's very possible that you could be affected on an unpatched machine. I assume that Apple will have this patched within a week.
If someone saw a link to a website containing a hilarious video of something happening to a Windows user and they decided to click on it and end up at this "specially-constructed Web page" would they still be safe because the rules had been relaxed?
No they would not be safe. The rules being laxed had nothing to do with the exploit. The attack can't happen remotely which is good, it requires user action. However, the user action is something we do all the time and don't realize it could happen. So it's a bad exploit. Going to a webpage is something most of us do 1000s of times a day.
Imagine if I posted a link on new photos of the iPhone! then I put some photos up but I also had this extra bit of code in there so you didn't even know you were exploited.
That's what makes this a bad exploit and it should be delt with soon.